This invention relates generally to the high pressure plasma oxidation of oxidizable layers, and more specifically to the oxidative removal of carbonaceous release layers in a high pressure oxygen plasma.
In the manufacture of many types of devices, the manufacturing process requires the removal of one material from the surface of a second material without deleteriously affecting the surface of that second material. Where one material is readily oxidizable and the other is not, that one material can sometimes be removed by oxidation. For example, in the manufacture of semiconductor devices, photoresist layers are often removed from the surface of a silicon wafer by oxidizing or "ashing" the photoresist material in an oxygen plasma. The plasma oxidation is done at a reduced pressure under conditions similar to those used for plasma etching and plasma deposition.
In a further example, as in the process for manufacturing polycrystalline silicon ribbons such as the process described in U.S. Pat. No. 4,370,288, polycrystalline silicon material is deposited onto a temporary refractory material substrate which is coated with a release layer of graphite. The silicon is separated from the temporary substrate, with the help of the release layer, by thermal expansion shear separation. During the process, however, a portion of the graphite release layer adheres to the silicon material and must be subsequently removed. The graphite material can be removed by sand blasting followed by chemical etching to remove the abrasive particulate contamination, but this process consumes large amounts of expensive abrasive material, requires a considerable amount of equipment maintenance, and is not a clean, contaminant free operation. The graphite layer can also be removed by thermal oxidation, for example, by subjecting the graphite material on the silicon to an oxidizing ambient for about 2 hours at a temperature in excess of 900.degree. C. This process is time-consuming, expensive, and requires that the silicon material be exposed to deleterious high temperatures for long periods of time. The large amount of graphite material can be removed by low pressure plasma oxidation only by extremely long exposures.
Similarly, other manufacturing operations using the same or similar materials require the removal of a first material from a second dissimilar material. In many of these operations the workpiece cannot he exposed to high temperatures for long periods of time to accomplish the removal. A need therefore existed for a process for such removal which would overcome the problem associated with the prior art processes.
It is therefore an object of this invention to provide an improved process for the oxidative removal of a material from the surface of a second, dissimilar material.
It is another object of this invention to provide an improved process for the high pressure plasma oxidative removal of carbonaceous material from the surface of another material.
It is yet another object of this invention to provide an improved process for the oxidative removal of a carbonaceous release material from a silicon ribbon.
It is a further object of this invention to provide an improved process for producing silicon ribbon.
It is a still further object of this invention to provide a low temperature process for the removal of an oxidizable layer from a dissimilar substrate.